1. Field of the Invention
This invention relates to an interleaved circuit of a flexure used in a disk drive for an information processing apparatus, such as a personal computer.
2. Description of the Related Art
A hard disk drive (HDD) is used in an information processing apparatus, such as a personal computer. The HDD comprises a magnetic disk rotatable about a spindle, a carriage turnable about a pivot, etc. A disk drive suspension is disposed on an arm of the carriage.
The disk drive suspension comprises a baseplate, load beam, etc. A flexure is disposed on the load beam. A slider is mounted on a gimbal portion formed near the distal end of the flexure. The slider is provided with elements (transducers) for accessing data, that is, for reading or writing data. The suspension, flexure, etc., constitute a head gimbal assembly.
Flexures are practically available in various forms depending on required specifications. A flexure with conductors is a known example. A circuit of the flexure of this type comprises a metal base, insulating layer formed on the metal base, a plurality of conductors formed on the insulating layer, etc. The metal base is formed of a thin stainless-steel plate. The insulating layer consists mainly of an electrically insulating material, such as polyimide. Each conductor is a copper member, one end of which is connected to en element (e.g., magnetoresistive element) of a slider. The other end of the conductor is connected to an amplifier or the like of a disk drive.
The circuit of the flexure is expected to be reduced in impedance, in order to match the amplifier with the element of the slider and reduce energy consumption. A reduction in inductance is also required. To achieve high-speed data transfer, moreover, such characteristics (low-attenuation characteristics) are required that the attenuation is low even in a high-frequency range.
These requirements can be effectively satisfied by a flexure with conductors that comprises multi-trace transmission lines. A circuit with multi-trace transmission lines is also called an interleaved circuit. A flexure comprising an interleaved circuit is disclosed in U.S. Pat. No. 5,717,547. Flexures with interleaved circuits are suitable for high-speed data transfer due to their low attenuation in a high-frequency band.
FIGS. 13 and 14 show an example of an interleaved circuit 100. This interleaved circuit 100 comprises two first branch conductors 101a and 101b branching from a first conductor 101 and two second branch conductors 102a and 102b branching from a second conductor 102. As shown in FIG. 14, an insulating layer 111 is formed on a metal base 110. All the branch conductors 101a, 101b, 102a and 102b are located on the insulating layer 111. These branch conductors 101a to 102b are covered by a cover resin layer 112.
Each of the conductors of the interleaved circuit shown in FIGS. 13 and 14 is bifurcated. However, an investigation conducted by the inventors of the present invention revealed that further impedance reduction can be achieved by increasing the number of branch conductors and minimizing the distance between the branch conductors.
In the conventional interleaved circuit, however, all the branch conductors are located on the same plane. In this arrangement, the distance between the branch conductors cannot be reduced unlimitedly, due to the use of resists for the formation of the branch conductors by etching or plating. In the prior art example (FIG. 14), all the branch conductors 101a to 102b are formed on the insulating layer 111. In this case, the width of a resist formed between each two adjacent branch conductors cannot be reduced unlimitedly. Thus, distance G0 between the branch conductors is 15 μm or more.
If all the branch conductors are located on the same plane of the insulating layer to reduce impedance, as described above, the interleaved circuit is so wide that the design flexibility of a flexure with conductors is limited.